Suction apparatus with noise reduction means

ABSTRACT

The invention concerns a suction apparatus with noise reduction means ( 7, 8 ) in one or more airflow passages ( 2, 3, 4 ) for reducing noise emission from an airflow generator ( 1 ) or the like, wherein at least one airflow passage ( 2, 3, 4 ) is provided with at least one indentation ( 7 ) with a predetermined depth (D) extending substantially perpendicularly to the general direction of the noise in the passage. By the invention, a suction apparatus with noise reduction means is provided which is simple and efficient at reducing noise and also inexpensive to manufacture.

[0001] The present invention relates to a suction apparatus with noisereduction means in one or more airflow passages for reducing noiseemission from an airflow generator or the like.

[0002] WO-A-97/13443 discloses a suction apparatus of theabove-mentioned kind where the airflow generator is enclosed in ahousing with an air inlet and an air outlet. The housing and the outletare provided with sound-absorbing foamed plastic materials. This meansthat a significant noise reduction and a compact silencer may beobtained by providing the housing volume and at the outlet flow passageswith a sound insulation material. Although this solution offers gooddampening of the noise emission, this noise reduction solution comprisesmany different components and is therefore somewhat troublesome toassemble and consequently relatively expensive to manufacture.

[0003] Another solution to the noise reduction problem is known fromEP-A-0 099 466, in which a vacuum cleaner is disclosed This vacuumcleaner is provided with a sound-absorbing foam material around themotor housing and around the inlet and outlet passages lined with asound-absorbing material. The outlet passages in this vacuum cleaner aredesigned with several changes in cross-section areas and with bends inorder to provide changes in the acoustical properties that lead toreflections of the noise. The vacuum cleaner is moreover provided with adampener in front of the air inlet. Although this solution can providean additional silencing effect, it is relatively extensive in dimensionsand complex in design, making it cumbersome and relatively expensive tomanufacture.

[0004] Another kind of noise reduction solution for a vacuum cleaner isknown from DE-A-40 37 442, in which an insert unit is inserted in theair outlet that directs the airflow through a serpentine-likeflow-pattern. This noise reduction solution takes up a considerableamount of space and has a somewhat limited noise-reducing effect. Also,as the air is repeatedly diverted in this manner, it may cause anundesired loss in pressure.

[0005] Another solution to noise reduction in a vacuum cleaner is knownfrom EP-A-0 289 987, in which the exhaust passage is provided with asilencing passage consisting of a number of concentric air-tight tubularribs defining a number of concentric exhaust airflow passages. A noiseabsorption material is provided along the upper walls of the passages.However, this solution is bulky in design and does not provide asatisfactory noise reduction.

[0006] Normally, the airflow generator is made up by an electric motorconnected to a blower, i.e. a radial ventilator. When the vacuum cleaneris only used for dry suction cleaning, the primary airflow through theblower is also used for cooling the electric motor. However, when thevacuum cleaner is designed for use in a wet environment, the motor mustbe cooled by a separate cooling ventilator. Both the blower and thecooling ventilator cause emission of noise. The noise extends to thesurroundings through the exhaust passage of the primary airflow and fromthe inlet and the exhaust air passages of the cooling air. Thesound-absorbing material may be provided in the airflow passages oraround the motor. However, the cooling ventilator is particularlydifficult to silence in this manner due to the relatively short airflowpassages. Furthermore, noise from the cooling ventilator is of a narrowband nature which makes it suitable for reduction by means of thedescribed technique.

[0007] From JP 06 035478 A and JP 06 030860 A some other solutionsconcerning noise reduction of vacuum cleaners are known where aresonance type acoustic filter is provided. However, although this has asilencing effect their design is somewhat space consuming just as theproduction of these acoustic filters as an integral part of the vacuumcleaner housing is difficult and expensive.

[0008] On this basis, it is an object of the invention to provide asuction apparatus with noise reduction means which is simple tomanufacture and with a compact structure so as to allow for a compactdesign of the device in which the airflow generator is installed.

[0009] This object is achieved by a suction apparatus of the initiallymentioned kind, wherein at least one airflow passage is provided with aplurality of indentations is arranged successively in the direction ofthe airflow, said indentations having a predetermined depth extendingsubstantially perpendicularly to the general direction of the noise inthe passage, and that the indentations are formed by providingprotruding wall members on at least one side of the flow passage.

[0010] By the invention, a suction apparatus with noise reduction meansis provided which is simple and efficient at reducing the noise and alsoinexpensive to manufacture. The noise is dampened as it extends in anairflow passage. A suction apparatus according to the invention issuitable for use in a vacuum cleaner with a separately cooled airflowgenerator by providing the airflow passages leading to the airflowgenerator and/or the ventilator with noise reduction means.

[0011] The principle at work by noise reduction according to theinvention is that part of the noise that extends in the passage willextend into the indentations. At the bottom of the indentation, thenoise will be reflected back into the passage. When the indentationshave a depth corresponding to a ¼ of the wave length of the noise, thenoise wave reflected by the bottom of the indentation may interferedestructively with the noise in the passage. Hereby, the noise will bereduced at particular frequencies as the reflected noise will cancel outthe noise in the passage, resulting in a considerable reduction in thenoise level.

[0012] the wall members are provided perpendicular to the direction ofthe airflow. The effect of the noise reduction is optimised when theheight or heights of the wall members or indentations is/are ¼+n×½ ofthe wave length of the noise to be reduced, where n is an integernumber, including n=0. Hereby, the indentations may be particularlysuitable for silencing noise at one or more predetermined frequencies bychoosing an appropriate depth of the indentations. However, noisereduction not only occurs at the predetermined frequencies but also atfrequencies in close proximity thereto.

[0013] A plurality of indentations is arranged successively in thedirection of the airflow, whereby an improved effect of the noisereduction is obtained in a simple manner and by a compact structure.Hereby, a noise filter may be integrally moulded in the parts making upthe housing of the suction apparatus.

[0014] Preferably, the indentations are sub-diverted intosub-indentations in the traverse direction of the general direction ofthe airflow. The width of the indentations generally corresponds to thelength and is shorter than the depth. Hereby, it is ensured that thenoise cannot travel “sideways” and fail to interfere with the remainingnoise in the passage.

[0015] In a preferred embodiment, the indentations are formed byproviding protruding wall members on at least one side of the flowpassage. Hereby, the noise reduction means may be integrally formed inthe housing members defining the airflow passages. When a plurality ofindentations is required, a plurality of wall members is provided. In aparticular embodiment, a grid of protruding wall members is provided inthe airflow passage.

[0016] In a first embodiment, the airflow generator is separately cooledand provided with noise reduction means in one or more of the airflowpassages. Alternatively, the airflow generator may be cooled by theprimary airflow generated.

[0017] The invention will be described in detail below with reference tothe accompanying drawings, in which

[0018]FIG. 1 is a schematic side view of a suction apparatus,

[0019]FIG. 2 is a principle illustration explaining the noise reductionprinciple according to the invention,

[0020]FIG. 3 is a cross-section view of a suction apparatus according toa first embodiment of the invention,

[0021]FIG. 4 is a perspective view of a lid part of a suction apparatuswith a noise reduction means according to a second embodiment of theinvention,

[0022]FIG. 5 is a detailed schematic view incorporating a thirdembodiment of the noise reduction principle according to the invention,and

[0023]FIG. 6 is a detailed schematic view incorporating a fourthembodiment of the invention.

[0024]FIG. 1 is a schematic view of a vacuum cleaner with a separatelycooled airflow generator 1. The airflow generator 1 comprises anelectric motor 5 connected to a blower 6 for generation of the primarysuction airflow in the suction hose 10. On top, the electric motor 5 isequipped with a cooling fan 12 for cooling the motor 5.

[0025] Airflow passages 2, 3, 4 and 10 are provided in association withthe blower 6 and the fan 12. The vacuum generated by the blower causes aprimary airflow through the air hose 13. This air is exhausted throughthe primary air outlet passage 4.

[0026] Air for cooling of the electric motor 5 is drawn in through aninlet passage 2 by the fan 12. The utilised cooling air is exhaustedthrough the cooling air outlet passage 3.

[0027] The noise generated by the airflow generator and/or by thevelocity of the airflow travels through the passages 2, 3, 4, 10 fromthe noise-emitting source and into the surroundings irrespective of thegeneral flow direction of the air (see arrow indications) in thepassages.

[0028] In order to reduce this noise emission, one or more of thepassages 2, 3, 4 may be provided with noise reduction means 7, 8. Anoise reduction means according to the invention comprises a repeatedstructure such as shown in FIG. 2. According to the invention, the noisereduction means involves a number of indentations 7 extending from oneof the passage walls substantially perpendicularly to the direction ofthe noise in the particular passage 2, 3, 4. The indentations 7 aresuccessively arranged in the direction of the airflow and are separatedby wall members 8. The indentations 7 are provided with a predetermineddepth D that generally corresponds to the frequency of the noise in thepassage to be silenced.

[0029] The depths of the indentations 7 may not necessarily be the samebut may vary in order to reduce noise over a broader range offrequencies. This, however, is achieved at the expense of a lessefficient noise reduction.

[0030] Part of the noise-travelling through the passage 2, 3, 4 willextend into the indentations 7. At the bottom of the indentations 7, thenoise is reflected back into the passage 2, 3, 4. The reflected noise isdelayed and is thus out of phase with the noise in the passage. Thisresults in a destructive interference of-the reflected noise and noisein the passage, generating a significant noise reduction. Thenoise-reducing effect is optimised when the noise has a frequency thatcorresponds to a indentation depth D of ¼, ¾, {fraction (5/4)}, etc. ofthe wave length. Moreover, the effect is also improved if theindentations extend across the entire width of the passage and/or ifseveral indentations are provided successively.

[0031] In a vacuum cleaner, the noise from the airflow generator is atits most intense level within the frequency range 1 kHz to 5 kHz. Thecooling ventilator in a separately cooled motor scatters noise at asomewhat higher frequency within in the range of 2 kHz to 7 kHz.

[0032] In table 1, the preferred depths D of the indentations 7 areindicated for dampening noise within a relevant frequency range: TABLE 1Indentation depths and their corresponding frequencies of maximumdampening corresponding to ¼, ¾ or {fraction (5/4)} of the wave length.Depth D Dampening at Dampening at Dampening at 86 mm 1 kHz 3 kHz 5 kHz43 mm 2 kHz 6 kHz — 17 mm 5 kHz — — 12 mm 7 kHz — —

[0033] As it appears from table 1, the indentation depth D—or height ofthe wall members 8—should preferably be between 17 mm and 86 mm.Increased depth is particularly advantageous, as it provides a dampeningeffect at more frequencies within the relevant frequency range.

[0034] A noise reduction means according to the invention isadvantageous as the noise reduction may be integrated in passagedefining parts of the vacuum cleaner and produced in a mouldable plasticmaterial by an injection moulding process. This means that no extrasound-absorbing elements need to be placed in the vacuum cleaner.

[0035] A first embodiment of the invention is shown in FIG. 3, where anumber of thin wall members 8 extend downwards from the top passage walland into the airflow passages 2, 3. Hereby, a number of indentations 7are formed between the thin wall members 8. The length of the thin wallmembers 8 (i.e. the depth D of the indentations 7) may vary, such asindicated in the figure, in order to adapt the noise reduction means todifferent frequencies.

[0036] In a second preferred embodiment, the top lid 9 of a vacuumcleaner is provided with a grid 11 of thin wall members 8 forming anumber of cells acting as noise-reducing indentations 7, see FIG. 4. Thegrid 11 may be integrally formed on the inside of the lid part 9. Byusing a grid, the indentations 7 are sub-divided so that noise isprevented from travelling “sideways” down into the grooves orindentations. The grid 11 is advantageous as it may be provided acrossthe entire width of a passage wall, causing a significant noisereduction.

[0037] Other embodiments of the invention are shown in FIGS. 5 and 6. InFIG. 5, the noise reduction may be performed in a relative short airexhaust passage 4. In FIG. 6, the lower passage wall is provided withnoise indentations separated by thin wall elements 14.

[0038] As it can be appreciated from the various embodiments, theprinciple of noise reduction according to the invention has a wide rangeof use and may be used to dampen noise in a vacuum cleaner which travelsthrough a passage irrespective of its origin.

1. A suction apparatus with noise reduction means (7, 8) in one or moreairflow passages (2, 3, 4) for reducing noise emission from an airflowgenerator (1) or the like, characterised in that at least one airflowpassage (2, 3, 4) is provided with a plurality of indentations (7)arranged successively in the direction of the airflow, said indentations(7) having a predetermined depth (D) extending substantiallyperpendicularly to the general direction of the noise in the passage (2,3, 4), and that the indentations (7) are formed by providing protrudingwall members (9) on at least one side of the flow passage (2, 3, 4). 2.A suction apparatus according to claim 1, wherein the heights of each ofthe wall members (8) are ¼ (2n+1) where λ is the wave length of thenoise to be reduced and n is an integer number, including n=0.
 3. Asuction apparatus according to claim 2, wherein the height of all thewall members (B) provided in an airflow passage (2, 3, 4) is the same.4. A suction apparatus according to claim 1 or 2, wherein the heights ofthe wall members (B) provided in an air flow passage (2, 3, 4) aredifferent in order to reduce noise at different frequencies.
 5. Asuction apparatus according to any of the preceding claims, wherein theindentations (7) are sub-diverted into sub-indentations in the traversedirection of the direction of the noise.
 6. A suction apparatusaccording to any of the preceding claims, wherein a plurality of wallmembers (8) of different thickness are provided.
 7. A suction apparatusaccording to any of the preceding claims, wherein the wall members (8)are provided perpendicular to the direction of the airflow.
 8. A suctionapparatus according to any of the preceding claims, wherein a grid (11)of protruding wall members (8) is provided in the airflow passage (2, 3,4).
 9. A suction apparatus according to any of the preceding claims,wherein the airflow generator (1) is separately cooled.